Process For Producing In Yeast Empty Viral Capsids Consisting Of Proteins Derived From Pvp2 Of The Infectious Bursal Disease Virus (Ibdv)

Abstract

The empty capsids of the infectious bursal disease virus (IBDV) are formed by the assembly of proteins derived from the pVP2 protein of IBDV, with a different size and with an application in producing vaccines and in preparing gene therapy vectors.

Description

FIELD OF THE INVENTION [0001] The invention relates to a process for producing empty viral capsids consisting of proteins derived from the protein pVP2 (pVP2*) of the infectious bursal disease virus (IBDV). Said capsids can be used in producing vaccines and in preparing gene therapy vectors. BACKGROUND OF THE INVENTION [0002] The infectious bursal disease virus (IBDV) is a member of the Birnaviridae family, which infects various avian species and is directly responsible for a severe immunosuppressive disease, causing economic losses in the avian industry worldwide (Sharma J M et al. 2000. Infectious bursal disease virus of chickens: pathogenesis and immunosuppression. Developmental and Comparative Immunology 24:223-235; van den Berg T P et al. 2000. Infectious bursal disease (Gumboro disease). Revue scientifique et technique (International Office of Epizootics) 19:509-543). [0003] IBDV particles are icosahedral with symmetry T=13, they lack the envelope and are formed by a single pr...

AI Technical Summary

Benefits of technology

[0019] These results have allowed designing a new strategy for producing the VLPs of IBDV provided by this invention (VLPs-pVP2*) which, unlike the methods previously described for producing VLPs of IBDV (generally based on the use of recombinant viruses derived from the vaccine virus or from a baculovirus and in producing said VLPs from mammal or insect cells, unacceptable production systems for the industrial production of veterinarian vaccines for biosafety, efficiency and cost reasons), allows expressing and producing VLPs of IBDV in yeasts thereby correcting the problems of biosafety and efficiency, and a significant reduction of production costs, which allows its use in the industrial production of vaccines against IBDV. Said strategy is based on the use of a gene expression system or vector which allows expressing a pVP2* of IBDV in yeasts and forming VLPs-pVP2* of IBDV, with a very high yield and very low economic cost.

[0020] The vaccines obtained by using said VLPs-pVP2* have several advantages since, on one hand, the handling of highly infectious material is avoided, the potential risk of the occurrence of new IBDV mutants is prevented and the use of a live virus in poultry farms is removed, thus preventing the risk of spreading vaccine strains of IBDV into the environment, and on the other hand, it allows the development of differential diagnostic systems to discriminate between vaccinated and infected animals. These differential diagnostic systems are based on detecting antibodies against VP2, VP3 and VP4 proteins of IBDV. Animals with IBDV develop a strong humoral response to both proteins, whereas animals immunized with VLPs-pVP2* only have antibodies against the VP2 protein of IBDV.

Problems solved by technology

Until now, the approaches aimed at obtaining an atomic model for IBDV particles have failed.

This latter type of vaccines has the typical drawbacks associated with the use of live attenuated vaccines, specifically, the risk of mutations reverting the virulence of the virus or making it lose its immunogenicity.

The results obtained in chicken immunization tests with said vaccines have not been completely satisfactory.

VLPs are obtained by self-assembly of all or part of the subunits constituting the viral capsid, and they mimic the structure and antigenic properties of the native virion, although they lack genetic material, so they are unable to replicate themselves.

The various processes for producing VLPs of IBDV hereinbefore described have several drawbacks which reduce or prevent their applicability in generating vaccines against IBDV given that: i) the vectors developed for the production of VLPs of IBDV are based on the use of recombinant viruses derived from the vaccine virus or baculovirus, so the production of said VLPs is carried out from mammal or insect cells; however, these production systems are very expensive for their application in the production at industrial level of veterinarian vaccines; ii) the production of VLPs of IBDV in mammal cells is based on the use of recombinants of the vaccine virus; however, in addition to the high cost of this production system, the use of a recombinant virus capable of infecting both mammals and birds does not meet the biosafety conditions necessary for its use as a vaccine; iii) in addition to the high cost of the production of VLPs of IBDV in insect cells using conventional expression systems, for example rBVs only expressing the viral polyprotein, it is very inefficient and leads to a virtually nule production of VLPs; and iv) the production of VLPs of IBDV in insect cells by means of the expression of a chimeric polyprotein, formed by the fusion of the open reading frame (ORF) corresponding to a heterologous protein at the 3′ end of the ORF corresponding to the IBDV polyprotein, results in the production of VLPs of IBDV containing a fusion protein (VP3-heterologous protein), which introduces a protein element not present in IBDV virions, with an unknown effect and doubtful applicability in the production chain of chicken meat for human consumption.

Yeasts are an alternative to the hereinbefore discussed expression systems due to simplicity and production costs.

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